MOSFET Safe Operating Limits – Keep It Cool, Keep It Safe
Whether you’re designing a motor driver, LED dimmer, or power supply, understanding MOSFET safe operating limits is critical. Pushing a MOSFET beyond its limits can cause overheating, failure, or even small explosions!
❗ The Problem: Exceeding MOSFET Ratings
MOSFETs have three key limits:
Drain-Source Voltage (V<sub>DS</sub>)
Continuous Drain Current (I<sub>D</sub>)
Maximum Power Dissipation (P<sub>D</sub>)
Ignoring any of these can lead to thermal runaway or breakdown of the device.
🛠️ The Solution: Stay Within the SOA
The Safe Operating Area (SOA) graph in a datasheet shows the voltage and current ranges the MOSFET can handle safely. You can calculate power loss and ensure you stay within thermal limits using a simple formula:
🔢 Sample Calculation
For a load switching 5A through a MOSFET with R<sub>DS(on)</sub> = 0.05Ω:
P = I² × R = 5² × 0.05 = 1.25W
To safely dissipate this, you’ll need a proper heatsink or thermal pad.
🧰 Practical Example: DIY Inverter Project
A prototyper used an IRFZ44N without checking current ratings. The MOSFET overheated and failed. Replacing it with a MOSFET rated at 50A and adding a heatsink solved the problem.
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